The invention relates to a nozzle structure for rocket nozzles having a cooled nozzle wall comprising a large number of closely spaced cooling channels extending from the inlet end of the nozzle to its outlet end.
Such cooled rocket nozzles must have a nozzle wall which is both light and strong and which provides a uniform cooling effect. To achieve this, a large number of parallel cooling channels are arranged in the wall material of metal itself. The cooling channels can be formed either by machining the wall material and supplemental design measures or the nozzle wall itself can be made of a large number of closely spaced tubes which are joined together.
Also, the wall can be formed of a compound layer of two materials in which by various methods cavities are made, which in the compounded state form the channels.
Rocket nozzles of the above-mentioned type are known from for example U.S. Pat. Nos. 5,221,045, 5,386,628, 5,233,755, 4,942,653 and 3,768,256.
In addition to the fact that it is labor-intensive and time-consuming to build a nozzle wall of a large numberxe2x80x94several hundredsxe2x80x94of thin tubes, such a nozzle also shows other drawbacks. Thus, it is hard to achieve the necessary strength of the structure in tangential direction if the tubes are joined to each other by brazing. Such tubes have also been diffusion bonded but reliable strength in tangential direction has not been reached.
In the case different ways of machining of the nozzle wall material are used to provide grooves or gutters which then are covered or combined with another layer of material to form the channels it is also difficult to make the final joining, for instance by welding, where the weld is exposed to the stress from the pressure of the coolant.
Another drawback of all the previously known nozzle structures is that the material used must have necessary strength and hence will have a relatively high density, such as stainless steel or nickel-based materials. Thus, the nozzles will be heavy. This is a great disadvantage, since the weight of the nozzle will reduce the payload capacity of the rocket.
The object of the invention is to eliminate the drawbacks of the prior art and to provide a rocket nozzle which is much easier and faster to produce, the strength of which is greatly improved, but also to provide a lighter nozzle.
This is achieved according to the invention in that the nozzle wall consists of several elongated panels which extend from the inlet end to the outlet end of nozzle and are joined together along their longitudinal side edges and in each of which is formed a number of said adjacent cooling channels, which extend in the longitudinal direction of the panels.
Obviously, this results in a significant saving of time in that there is no need for the laborious work to put a large number of narrow tubes together and then join them along their length.
Since the cooling channels are arranged in panels, it has been found that according to a first embodiment of the invention, the panels for a nozzle wall structure for regeneratively cooled rocket nozzles can be made of a metal totally different from what has been used before, namely a metal that can be extruded, such as aluminium, alloys of aluminium or copper. This means that an additional simplification and saving of time is achieved. Regarding in the first place aluminium, the necessary strength of the panels can be ensured by a certain dimensional increase compared to stainless steel or nickel-based materials, but the total weight per surface unit will still be less than for said materials.
Experiments and calculations have proved that the high thermal conductivity, particularly of aluminium, makes the risk for overheating and melting, particularly at certain points, more or less non-existent. If necessary the inside of the nozzle can be coated with a ceramic thermal barrier coating as is known in the art.
The high thermal conductivity of the proposed materials makes the thermal stresses low. The structure of the nozzle remains elastic during the whole load cycle. The design and development of the nozzle is simplified by this.
According to a second embodiment of the invention the panel made of extrudable metal can be manufactured of two extruded panel parts, which are provided with suitable interengaging means, so that said panel parts will be locked together when said interengaging means are pushed axially into each other.